Multilayer ceramic capacitor

ABSTRACT

A multilayer ceramic capacitor includes: a pair of external electrodes; a first internal electrode containing a base metal and coupled to one of the external electrodes; a dielectric layer stacked on the first internal electrode and containing the base metal and a ceramic material mainly composed of barium titanate; and a second internal electrode stacked on the dielectric layer, containing the base metal, and coupled to another one of the external electrodes, wherein a concentration of the base metal in each of five regions, which are equally divided regions between locations 50 nm away from the first and second internal electrodes in a stacking direction between the first and second internal electrodes, is within ±20% of an average of the concentrations of the base metal in the five regions, and an atomic concentration ratio of Mg to Ti is 0 or greater and less than 0.002 in the dielectric layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2016-122000, filed on Jun. 20,2016, the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the present invention relates to a multilayerceramic capacitor.

BACKGROUND

To achieve small-sized large-capacity multilayer ceramic capacitors,dielectric layers have been thinned and the number of stacked dielectriclayers has been increased. The design of dielectric layers thatdetermine the characteristics of the multilayer ceramic capacitor isimportant. For example, disclosed is a technique that diffuses Ni into 3to 30% of the distance between internal electrodes to improve thetemperature characteristic of the capacitance (see Japanese PatentApplication Publication No. 10-4027, for example).

However, in the above described technique, a base metal is not diffusedin the middle portion of the dielectric layer in the stacking direction,and therefore, the concentration of the base metal may be partially highin the stacking direction. The part with a high concentration of thebase metal decreases the permittivity of the dielectric layer.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided amultilayer ceramic capacitor including: a pair of external electrodes; afirst internal electrode that contains a base metal and is coupled toone of the pair of external electrodes; a dielectric layer that isstacked on the first internal electrode and contains the base metal anda ceramic material mainly composed of barium titanate; and a secondinternal electrode that is stacked on the dielectric layer, contains thebase metal, and is coupled to another one of the pair of externalelectrodes, wherein a concentration of the base metal in each of fiveregions is within ±20% of an average of the concentrations of the basemetal in the five regions, the five regions being obtained by dividing aregion from a location 50 nm away from the first internal electrode ofthe dielectric layer to a location 50 nm away from the second internalelectrode of the dielectric layer in a stacking direction between thefirst internal electrode and the second internal electrode equally intofive, and an atomic concentration ratio of Mg to Ti is equal to orgreater than 0 and less than 0.002 in the dielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional perspective view of a multilayerceramic capacitor;

FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1;

FIG. 3 is a partial enlarged view of FIG. 2;

FIG. 4 illustrates crystal grains and a crystal grain boundary;

FIG. 5 is a flowchart illustrating a method of manufacturing themultilayer ceramic capacitor; and

FIG. 6 illustrates examples and comparative examples.

DETAILED DESCRIPTION

A description will be given of an embodiment with reference to theaccompanying drawings.

EMBODIMENT

A multilayer ceramic capacitor will be described. FIG. 1 is a partialcross-sectional perspective view of a multilayer ceramic capacitor 100.As illustrated in FIG. 1, the multilayer ceramic capacitor 100 includesa multilayer chip 10 having a rectangular parallelepiped shape, andexternal electrodes 20 and 30 that are located on opposing end faces ofthe multilayer chip 10.

The external electrodes 20 and 30 contain a base metal material. Themultilayer chip 10 has a structure designed to have dielectric layers11, which contain a ceramic material functioning as a dielectric, andinternal electrode layers 12, which contain a base metal material,alternately stacked. The end edges of the internal electrode layers 12are alternately exposed to the end face, on which the external electrode20 is located, of the multilayer chip 10, and to the end face, on whichthe external electrode 30 is located, of the multilayer chip 10.Accordingly, the internal electrode layers 12 are alternatelyelectrically coupled to the external electrode 20 and to the externalelectrode 30. This structure allows the multilayer ceramic capacitor 100to have a structure in which a plurality of the dielectric layers 11 arestacked across the internal electrode layers 12. Additionally, in themultilayer chip 10, both end faces in the stacking direction of thedielectric layers 11 and the internal electrode layers 12 (hereinafter,referred to as the stacking direction) are covered with cover layers 13.The material of the cover layer 13 is, for example, the same as thematerial of the dielectric layer 11.

The multilayer ceramic capacitor 100 has, for example, a length of 0.2mm, a width of 0.1 mm, and a height of 0.3 mm, or a length of 0.6 mm, awidth of 0.3 mm, and a height of 0.3 mm, or a length of 1.0 mm, a widthof 0.5 mm, and a height of 0.5 mm, or a length of 3.2 mm, a width of 1.6mm, and a height of 1.6 mm, or a length of 4.5 mm, a width of 3.2 mm,and a height of 2.5 mm, but the dimensions are not limited to the abovedimensions.

The external electrodes 20 and 30 and the internal electrode layer 12are mainly composed of a base metal such as nickel (Ni), copper (Cu), ortin (Sn). The dielectric layer 11 is mainly composed of a ceramicmaterial having a perovskite structure expressed by a general expressionABO₃. The perovskite structure includes ABO_(3-α) having anoff-stoichiometric composition. The base metal contained in the internalelectrode layer 12 is diffused into the dielectric layer 11 in the formof an oxidized material. Accordingly, the base metal is distributed inthe dielectric layer 11. When the concentration of the base metal ispartially high in the stacking direction in the dielectric layer 11, thepermittivity decreases. Thus, in the following embodiment, a descriptionwill be given of a multilayer ceramic capacitor that can inhibit thedecrease in permittivity. As an example, the embodiment will focus on Nias the base metal contained in the internal electrode layer 12, and onBaTiO₃ (barium titanate) as the ceramic material with a perovskitestructure contained in the dielectric layer 11.

FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1. Thedielectric layer 11 sandwiched between two internal electrode layers 12,one of which is coupled to the external electrode 20 and the other ofwhich is coupled to the external electrode 30, has a uniform Niconcentration in the stacking direction. Thus, the region partiallyhaving a high Ni concentration is inhibited from existing in thedielectric layer 11. As a result, the decrease in permittivity of thedielectric layer 11 can be inhibited. In addition, the inhibition of thedecrease in permittivity of the dielectric layer 11 stabilizes thecapacitance of the multilayer ceramic capacitor 100 in which a pluralityof the dielectric layers 11 are stacked. As a result, variability incapacitance among a plurality of the multilayer ceramic capacitors 100can be reduced. As a result, reduced is a capacitance anomaly that thecapacitance does not fall even within the lower 20% range of the normaldistribution of the average capacitances of products and deviates fromthe normal distribution. As a result, the capacitance anomaly that thecapacitance unexpectedly falls below the lower limit of the allowablelimits of the capacitance can be reduced.

Next, the term “uniform Ni concentration” will be described. FIG. 3 is apartial enlarged view of the cross-section of the multilayer ceramiccapacitor 100, schematically enlarging any of areas indicated by circlesin FIG. 2. Hatching is omitted. As illustrated in FIG. 3, in thestacking direction between opposing surfaces of adjacent two internalelectrode layers 12, a region from a location 50 nm away from one of theinternal electrode layers 12 to a location 50 nm away from the other ofthe internal electrode layers 12 is virtually divided into five equalregions. Two measurement regions closest to the internal electrodelayers 12 are referred to as end portions 1, and the central measurementregion is referred to as a central portion 3, and measurement regionsbetween the end portions 1 and the central portion 3 are referred to asend portions 2. The Ni concentration of the dielectric layer 11 in thestacking direction between two adjacent internal electrode layers 12 isdefined to be uniform when the Ni concentrations of each of fivemeasurement regions obtained by division into five equal regions arewithin ±20% of the average of the Ni concentrations in the fivemeasurement regions. The reason for using the region located 50 nm awayfrom the internal electrode layers 12 is because the reflection by Ni ofthe internal electrode layer 12 may prevent the accurate measurement. Inaddition, the width of the measurement region is made to be 1 to 1.5times the thickness of the dielectric layer 11 in the stackingdirection. The both end faces in the stacking direction of thedielectric layer 11 of each measurement region are located in a regionwhere the adjacent two internal electrode layers 12 overlap with eachother in plan view over the entire region. The two adjacent internalelectrode layers here mean the electrodes producing a capacitance. Thatis, the two adjacent internal electrode layers are internal electrodelayers one of which is coupled to the external electrode 20 and theother of which is coupled to the external electrode 30.

A description will next be given of a measurement method of the Niconcentration. The Ni concentration can be calculated by measuring a Niatom distribution in the stacking direction of the dielectric layer 11.The Ni atom distribution can be measured with a transmission electronmicroscope or the like. For example, a TEM-EDS (TEM JEM-2100Fmanufactured by JEOL Ltd.), an EDS detector (JED-2300T manufactured byJEOL Ltd.) or the like can be used. Samples for the measurement can bemade by mechanically polishing (polishing in a plane normal to theinternal electrode layer) a reoxidized multilayer ceramic capacitor, andthinning the resulting multilayer ceramic capacitor by ion milling. Forexample, five samples with a thickness of 0.05 μm for five measurementregions may be made. If a sample that allows five measurement regions tobe measured with the sample alone is made, the measurement that canreduce variations can be performed.

For example, a transmission electron microscope with a probe diameter of1.5 nm scans and measures each measurement region over the entire rangeto measure the Ni concentration of each measurement region. To avoid theeffect of variations in thickness of the sample, an atomic concentrationratio Ni/(Ba+Ti) is used as the Ni concentration. That is, the Niconcentration, i.e., the abundance ratio of Ni to (Ba+Ti), can bemeasured by measuring the abundance of Ni atoms, Ba atoms, and Ti atomsby a transmission electron microscope or the like. The tip portion ofthe internal electrode layer 12 and an anomalous point at which depositsaggregate in the dielectric layer 11 are excluded from the Niconcentration measurement. For example, an area containing a compositiondifferent from that of the parent phase and having a diameter of 50 nmor greater is excluded from the measurement regions. Such a location is,for example, a location in which compounds containing Si, compoundscontaining Mn, or compounds containing Ni—Mg aggregate to exist.Alternatively, such a location is a location where the abundance ratioof Ba and Ti is 90% or less.

For example, the count numbers of (Ni_Kα), (Ba_Lα), and (Ti_Kα) areobtained from an STEM-EDS spectrum, and are normalized by dividing themby respective sensitivity factors (respective k factors) used in theCliff-Lorimer method. When the count number of (Ni_Kα)=I(Ni), the countnumber of (Ba_Lα)=I(Ba), and the count number of (Ti_Kα)=I(Ti), the Niconcentration={I(Ni)/k(Ni)}/{I(Ba)/k(Ba)+I(Ti)/k(Ti)}. Where k(Ni),k(Ba), and k(Ti) are sensitivity factors for normalization.

Then, based on the normalized values, the Ni concentration is calculatedby the normalized value of (Ni_Kα)/{the normalized value of (Ba_Lα)+thenormalized value of (Ti_Kα)}. In each region, the measurement isperformed till the intensity of (Ba_Lα)+(Ti_Kα) exceeds 500,000 counts.The JED Series Analysis Program manufactured by JEOL Ltd. can be used tocalculate the Ni concentration from the STEM-EDS spectrum.

Mg in the dielectric layer 11 has a function that inhibits the diffusionof the base metal contained in the internal electrode layer 12 in thedielectric layer 11. Thus, the dielectric layer 11 is made not tocontain Mg or is made to have an Mg concentration, i.e., an atomicconcentration ratio of Mg to Ti, equal to or greater than 0 and lessthan 0.002. The Mg concentration within the above range facilitates thediffusion of the base metal in the dielectric layer 11. Accordingly, theNi concentration in the dielectric layer 11 can be made to be moreuniform.

The Mg concentration in the dielectric layer 11 can be obtained bymeasuring the molar concentration of Mg when the molar concentration ofTi is made to be 1 with use of, for example, an Inductively CoupledPlasma (ICP) measurement method.

To facilitate the diffusion of Ni sufficiently, the thickness of thedielectric layer 11 is preferably small. Thus, the dielectric layer 11preferably has a thickness of 1.0 μm or less. On the other hand, fromthe viewpoints of withstand voltage, the thickness of the dielectriclayer 11 is preferably large. Thus, the dielectric layer 11 preferablyhas a thickness of 0.4 μm or greater.

The thicknesses of the dielectric layer 11 and the internal electrodelayer 12 can be measured as follows, for example. First, the centralportion of the multilayer ceramic capacitor 100 is cut by ion milling sothat the cross-section illustrated in FIG. 2 is exposed. Then, theexposed cross-section is photographed by a scanning electron microscope(SEM), and the thicknesses of the dielectric layer 11 and the internalelectrode layer 12, i.e., the dimensions in the stacking direction, arethen measured based on the resulting photo. An SEM photo is taken sothat the view angle of the SEM photo is 10 to 30 μm in both length andwidth, and the thicknesses of the dielectric layer 11 and the internalelectrode layer 12 of several locations located every 3 μm are measured,and the averages of the measured values are specified to be thethicknesses of the dielectric layer 11 and the internal electrode layer12. Twenty locations are measured in each of five different fields ofview to obtain 100 sets of data, and the average of the measured valuesis specified to be the layer thickness.

It is preferable that 80% or more of a plurality of the dielectriclayers 11 stacked in the multilayer ceramic capacitor 100 have a uniformNi concentration in the stacking direction, and the Mg concentration inthe dielectric layer 11 is equal to or greater than 0 and less than0.002. This is because the Ni concentration of the dielectric layer isuniformized in whole in the stacking direction of the multilayer ceramiccapacitor 100, and the capacitance of the multilayer ceramic capacitor100 thereby stabilizes. In this case, variability in capacitance among aplurality of the multilayer ceramic capacitors 100 can be reduced.

In the present embodiment, when 80% or more of a plurality of thedielectric layers 11 stacked in the multilayer ceramic capacitor 100have a uniform Ni concentration in the stacking direction, the Niconcentration of the overall dielectric layer in the stacking directionof the multilayer ceramic capacitor 100 is defined to be uniform. Forexample, as indicated by circles in FIG. 2, when the Ni concentrationsof at least four dielectric layers 11 out of five dielectric layers 11located in different locations in the stacking direction are uniform, itcan be judged that 80% or more of the dielectric layers 11 have auniform Ni concentration. In the multilayer ceramic capacitor 100, whenthe Ni concentrations of the dielectric layers 11 located in differentlocations in the stacking direction are uniform, the capacitance of themultilayer ceramic capacitor 100 stabilizes. Accordingly, variability incapacitance among a plurality of the multilayer ceramic capacitors 100can be reduced. Therefore, reduced is a capacitance anomaly that thecapacitance does not fall even within the lower 20% range of the normaldistribution of the average capacitances of products and deviates fromthe normal distribution.

It is preferable that when 90% or more of a plurality of the dielectriclayers 11 stacked in the multilayer ceramic capacitor 100 have a uniformNi concentration in the stacking direction, the Ni concentration of theoverall dielectric layer in the stacking direction of the multilayerceramic capacitor 100 is defined to be uniform. For example, asindicated by circles in FIG. 2, when all the Ni concentrations of fivedielectric layers 11 located in different locations in the stackingdirection are uniform, it can be judged that 90% or more of thedielectric layers 11 have a uniform Ni concentration.

When a crystal grain boundary exists in the above five measurementregions, the Ni concentration in a crystal grain and the Niconcentration of the crystal grain boundary adjacent to the crystalgrain are preferably equal to each other. In this case, variations in Niconcentration, which tends to be segregated in the crystal grainboundary, are reduced, and the Ni concentration in the stackingdirection of the dielectric layer 11 can be made to be further uniform.For example, as illustrated in FIG. 4, in a crystal grain, the Niconcentration can be measured by scanning a 50-nm square area (a hatchedpart in FIG. 4) over the entire range by a transmission electronmicroscope or the like using the above-described measurement method. Ina crystal grain boundary, using the above-described method, the crystalgrain boundary adjacent to the crystal grain is measured at, forexample, ten points (points indicated by circles in FIG. 4) with a 1.5nm probe, and the average of the obtained Ni concentrations can bemeasured as the Ni concentration of the crystal grain boundary. When theNi concentration in the crystal grain is within ±20% of the Niconcentration of the crystal grain boundary, both the Ni concentrationsare defined to be equal to each other.

As illustrated in FIG. 2, when the Ni concentration in a crystal grainand the Ni concentration of the crystal grain boundary adjacent to thecrystal grain are equal in 80% or more of a plurality of the dielectriclayers 11 stacked in the multilayer ceramic capacitor 100, the Niconcentration in a crystal grain and the Ni concentration of the crystalgrain boundary adjacent to the crystal grain are defined to be equalacross the multilayer ceramic capacitor 100. For example, as illustratedin FIG. 2, when the Ni concentration in a crystal grain and the Niconcentration of the crystal grain boundary adjacent to the crystalgrain are equal in at least four out of five dielectric layers 11located in different locations in the stacking direction, it can bejudged that the Ni concentration in a crystal grain and the Niconcentration of the crystal grain boundary adjacent to the crystalgrain are equal in 80% or more of a plurality of the dielectric layers11. When the Ni concentration in a crystal grain and the Niconcentration of the crystal grain boundary adjacent to the crystalgrain are equal over the entire range of the multilayer ceramiccapacitor 100, the capacitance of the multilayer ceramic capacitor 100further stabilizes. Accordingly, variability in capacitance among aplurality of the multilayer ceramic capacitors 100 can be furtherreduced. Therefore, reduced is a capacitance anomaly that thecapacitance does not fall even within the lower 20% range of the normaldistribution of the average capacitances of products and deviates fromthe normal distribution. Abnormal locations (for example, locations atwhich many segregations are aggregated), which seem evidently not totypify the product or the lot subjected to the measurement, are excludedfrom the measurement locations, and the segregation locations in which asecondary phase exists are excluded from the measurement. For example, aan area having a composition different from that of the parent phase andhaving a diameter of 50 nm or greater is not employed as a measurementregion. Examples of such locations are locations in which compoundscontaining Si, compounds containing Mn, or compounds containing Ni—Mgare aggregated to exist. Another example of such locations is a locationwhere the abundance ratio of Ba and Ti is 90% or less.

The dielectric layer 11 has been described as having a uniform Niconcentration in the stacking direction, but the Ni concentration in thedielectric layer 11 is approximately, for example, from 0.015 to 0.045.

To further inhibit the occurrence of the capacitance anomaly, it ispreferable that the Ni concentration of the dielectric layer 11 in thestacking direction between two adjacent internal electrode layers 12 isdefined to be uniform when individual Ni concentrations of the abovefive measurement regions are within preferably ±10%, more preferably ±5%of the average of the Ni concentrations of the five measurement regions.In addition, the above description has focused attention on BaTiO₃ as adielectric and on Ni as a base metal, but does not intend to suggest anylimitation. Since the permittivity decreases if other dielectrics alsohave a region in which the concentration of the base metal is partiallyhigh, the above-described embodiment can be applied to other dielectricsand other base metals.

A description will next be given of a manufacturing method of themultilayer ceramic capacitor 100. FIG. 5 is a flowchart illustrating amethod of manufacturing the multilayer ceramic capacitor 100.

Raw Powder Preparation Process

First, as illustrated in FIG. 5, raw powder for forming the dielectriclayer 11 is prepared. Ba and Ti contained in the dielectric layer 11 arenormally contained in the dielectric layer 11 in the form of a sinteredcompact of particles of BaTiO₃. BaTiO₃ is a tetragonal compound having aperovskite structure, exhibiting a high permittivity. BaTiO₃ is normallyobtained by reacting a titanium raw material such as titanium dioxidewith a barium raw material such as barium carbonate to synthesize bariumtitanate. There have been known many kinds of methods such as, forexample, the solid phase method, the sol-gel method, and thehydrothermal method as a method of synthesizing BaTiO₃. The presentembodiment can employ any of these methods.

Specified additive compounds may be added to resulting ceramic powderaccording to the purpose. The examples of the additive compounds includeMg, Mn, V, Cr, oxidation materials of rare-earth elements (Y, Dy, Tm,Ho, Tb, Yb, and Er), and oxidation materials of Sm, Eu, Gd, Co, Li, B,Na, K, and Si, or glass. In the present embodiment, Mg is added so thatthe Mg concentration in the ceramic powder is equal to or greater than 0and less than 0.002.

In the present embodiment, preferably, a compound containing an additivecompound is mixed with particles of BaTiO₃, and the resulting mixture iscalcined at 820 to 1150° C. Then, the resulting particles of BaTiO₃ arewet blended with the additive compound, dried, and ground to prepareceramic powder. For example, particles of BaTiO₃ obtained by the abovedescribed method and used to manufacture the multilayer ceramiccapacitor 100 of the present embodiment preferably have an averageparticle size of 50 to 150 nm to make the dielectric layer 11 thinner.For example, the particle size of the ceramic powder obtained asdescribed above may be adjusted by grinding treatment as necessary, ormay be controlled in combination with a classification treatment.

Stacking Process

Next, a binder such as polyvinyl butyral (PVB) resin, an organic solventsuch as ethanol or toluene, and a plasticizer such as dioctyl phthalate(DOP) are added to the resulting ceramic powder and wet-blended. Withuse of the resulting slurry, a strip-shaped dielectric green sheet witha thickness of 0.8 μm or less is coated on a base material by, forexample, a die coater method or a doctor blade method, and then dried.

Then, a conductive metal paste containing an organic binder is printedon the surface of the dielectric green sheet by screen printing orgravure printing to arrange patterns of internal electrode layersalternately led out to a pair of external electrodes of differentpolarizations. For the metal of the conductive metal paste, used is Niwith a purity of 99% or greater. BaTiO₃ with an average particle size of50 nm or less may be homogeneously distributed as a co-material into theconductive metal paste. The conductive metal paste approximately has aNi concentration of 50 mass %, and the internal electrode layer 12 aftercalcination approximately has a Ni concentration of 95 mass %.

Then, the dielectric green sheet on which the internal electrode layerpattern is printed is stamped into a predetermined size, and apredetermined number (for example, 200 to 500) of stamped dielectricgreen sheets are stacked while the base material is peeled so that theinternal electrode layers 12 and the dielectric layers 11 are alternatedwith each other and the end edges of the internal electrode layers arealternately exposed to both end faces in the length direction of thedielectric layer so as to be alternately led out to a pair of externalelectrodes of different polarizations.

Cover sheets, which are to be the cover layers 13, are pressed to bebonded at the top and bottom of the stacked dielectric green sheets, andcut into a predetermined chip size (for example, 1.0×0.5 mm). Thisprocess allows the molded body of the multilayer chip 10 to be obtained.

First Calcination Process

The molded body of the multilayer chip 10 obtained as described above isdebindered in an N₂ atmosphere, at 250 to 500° C., and is then calcinedin a reducing atmosphere (with an oxygen partial pressure of 10⁻⁵ to10⁻⁷ Pa), at 1100 to 1300° C. for ten minutes to two hours. This processcauses the compounds constituting the dielectric green sheets to besintered, growing grains of the compounds. As described above, obtainedis the multilayer ceramic capacitor 100 including the multilayer chip 10formed of the dielectric layers 11 and the internal electrode layer 12that are made of a sintered compact and alternately stacked thereinside,and the cover layers 13 formed as the outermost layers at the top andthe bottom in the stacking direction.

Second Calcination Process

Then, second calcination is performed as a heat treatment for diffusingNi in the internal electrode layer 12 into the dielectric layer 11. Themultilayer ceramic capacitor 100 is heat treated at 1000 to 1200° C.,which is lower than the temperature of the first calcination by 50 to100° C., at an oxygen partial pressure of 10⁻³ to 10⁻⁶ Pa for about twoto four hours. The calcination at an oxygen partial pressure higher thanthat of the first calcination facilitates oxidation of Ni, andsufficiently diffuses Ni into the dielectric layer 11. On the otherhand, since the temperature is lower than that of the first calcination,grain growth in the dielectric layer 11 is inhibited. Accordingly, thedielectric layer 11 is to have a uniform Ni concentration in thestacking direction.

Third Calcination Process

Then, as a reoxidation calcination, performed is third calcination (areoxidation treatment) at 600 to 1000° C., at an oxygen partial pressureof 10⁻² to 10 Pa for about one hour. In the third calcination process,since the oxygen partial pressure is high, Ni is oxidized, but the Niconcentration in the dielectric layer 11 does not change because thecalcination temperature range is lower than that of the secondcalcination process.

When the temperature and time for calcination are insufficient, thediffusion of Ni may be inhomogeneous. Thus, the temperature and time ofthe calcination reaction are preferably appropriately adjusted dependingon the component size and the number of layers. The external electrodes20 and 30 may be formed by, for example, calcining the multilayer chip10 formed by stacking the dielectric layers 11 and the internalelectrode layers 12, and then baking a conductive paste on both endportions of the multilayer chip 10. Alternatively, the conductive pastemay be applied before the second calcination, and baked simultaneouslyat the time of second calcination. The external electrodes may bethickly formed on both end faces of the multilayered body by sputtering.

In addition to the above-described manufacturing method, Ni can behomogeneously formed in the dielectric layer 11 by adding NiO to slurrywhen the slurry is formed. The Ni concentration may be made to beuniform only by a technique that adds NiO to slurry when the slurry isformed. Alternatively, a method that diffuses Ni into the dielectriclayer from the internal electrode by adding NiO to slurry and thenperforming the above-described second calcination process may beemployed.

EXAMPLES

The multilayer ceramic capacitors in accordance with the embodiment weremade to examine the characteristics.

Examples 1 to 12

The multilayer ceramic capacitors 100 were made in accordance with themanufacturing method in accordance with the above-described embodiment.Table 1 lists the structure common to examples 1 to 12. The externalelectrodes 20 and 30 are formed on both end portions of the multilayerchip 10, and have a structure including a Cu portion (with a thicknessof 22 μm), a Ni portion (with a thickness of 2 μm) formed on the Cuportion by plating, and an Sn portion (with a thickness of 6 μm) formedon the Ni portion by plating. The central portion of the multilayerceramic capacitor 100 was cut by ion milling so that the cross-sectionillustrated in FIG. 2 was exposed, and the exposed cross-section wasphotographed by a scanning electron microscope (SEM). Then thethicknesses of the dielectric layer 11 and the internal electrode layer12, i.e., the dimensions in the stacking direction, were measured basedon the resulting photo. An SEM photo was taken so that the view angle ofthe SEM photo was 10 to 30 μm in both length and width, and thethicknesses of the dielectric layer 11 and the internal electrode layer12 at several locations located every 3 μm were measured. Then, theaverages of the measured thicknesses were calculated as the thicknessesof the dielectric layer 11 and the internal electrode layer 12. Twentylocations were measured in five different fields of view to obtain 100sets of data, and the averages of them were specified to be thethicknesses of the dielectric layer 11 and the internal electrode layer12.

TABLE 1 Dimensions (mm) 1.0 × 0.5 × 0.5 Length × Width × Height Numberof dielectric layers 200 Thickness of the internal electrode 0.8 μmThickness of the external electrode  30 μm (including plating) Relativepermittivity 2000 to 4800

In the examples 1 to 12, in the first calcination process, the moldedbody of the multilayer chip 10 was debindered in an N₂ atmosphere, at250 to 500° C., and then calcined in a reducing atmosphere with anoxygen partial pressure of 5.0×10⁻⁶ Pa, at 1200° C. for one hour tocause the compounds constituting the dielectric green sheets to besintered to grow grains of the compounds. Then, in the secondcalcination process, the multilayer ceramic capacitor 100 was calcinedin a reducing atmosphere with an oxygen partial pressure of 5.0×10⁻⁵ Pa,at 1100° C., which is 100° C. lower than the temperature of the firstcalcination process, for three hours to diffuse Ni in the internalelectrode into the dielectric layer. Then, the third calcination processwas performed. In the examples 1 to 4, Mg was not added to thedielectric layer 11. In the examples 5 to 12, Mg was added to thedielectric layer 11.

In comparative examples 1 and 2, in the first calcination process, themolded body of the multilayer chip 10 was debindered in an N₂atmosphere, at 250 to 500° C., and then calcined in a reducingatmosphere with an oxygen partial pressure of 5.0×10⁻⁶ Pa, at 1200° C.for one hour to cause the compounds constituting the dielectric greensheet to be sintered to grow grains of the compounds. Then, the secondcalcination process was skipped and the third calcination process wasperformed. In the comparative examples 1 and 2, Mg was added.

Ten thousand samples were made for each of the examples 1 to 12 and thecomparative examples 1 and 2.

For the examples 1 to 12 and the comparative examples 1 and 2, the Niconcentration of the dielectric layer 11 was measured. As describedabove, in the stacking direction, a region from a location 50 nm awayfrom one internal electrode layer 12 and to a location 50 nm away fromthe other internal electrode layer 12 was virtually divided into fiveequal regions. The width in the direction perpendicular to the stackingdirection was made to be 1.2 times the thickness of the dielectriclayer, and the Ni concentrations of the obtained five measurementregions were measured. The adjacent two internal electrode layers 12overlap each other in plan view as effective electrodes across theentire surfaces of both end faces in the stacking direction of eachmeasurement region.

For the measurement of the Ni concentration, a TEM-EDS (TEM JEM-2100Fmanufactured by JEOL Ltd.) and an EDS detector (JED-2300T manufacturedby JEOL Ltd.) were used. Samples for measurement were made bymechanically polishing (polishing in a plane normal to the internalelectrode layer) a reoxidized multilayer ceramic capacitor and thinningthe polished multilayer ceramic capacitor by ion milling. Samples with athickness of 0.05 μm were made so that five measurement regions could bemeasured. Each measurement region was scanned and measured with a probediameter of 1.5 nm, and the Ni concentration of each measurement regionwas measured. To measure the Ni concentration, the Ni concentration wascalculated from an STEM-EDS spectrum using the JED Series AnalysisProgram manufactured by JEOL Ltd. as described above. When theindividual Ni concentrations of the five measurement regions are within±20% of the average of the Ni concentrations of the measurement regions,the Ni concentration of the dielectric layer 11 in the ceramic capacitorwas considered to be uniform. In the multilayer ceramic capacitor 100,when the Ni concentrations of at least four dielectric layers 11 of fivedifferent dielectric layers 11 were uniform, the Ni concentration of theoverall dielectric layer in the stacking direction of the multilayerceramic capacitor 100 was considered to be uniform.

In addition, the Mg concentration in the dielectric layer 11 wasobtained by measuring the molar concentration of Mg when Ti was made tobe 1 with use of the Inductively Coupled Plasma (ICP) measurementmethod.

Analysis

FIG. 6 lists whether the Ni concentration is uniform or non-uniform. Aspresented in FIG. 6, in the examples 1 to 12, the Ni concentration ofthe overall dielectric layer 11 in the stacking direction of themultilayer ceramic capacitor 100 was uniform. In the comparativeexamples 1 and 2, the Ni concentration of the dielectric layer in thestacking direction of the multilayer ceramic capacitor 100 did notbecome uniform. The diffusion of Ni mainly proceeds in the secondcalcination process, and the diffusion is likely to proceed in the formof nickel oxide (NiO). The oxygen partial pressure in the secondcalcination process of the examples 1 to 12 was 5.0×10⁻⁵ Pa, and thiscondition is considered a condition that Ni is easily diffused becausethe atmosphere is an atmosphere in which nickel oxide is easilyproduced.

In FIG. 6, the number in the column of “number of uniform locations”presents the number of locations in which the Ni concentration wasjudged to be uniform in five different locations at which the dielectriclayer was measured. The column of “most deviated region” represents thelocation of the measurement region of which the Ni concentrationdeviated from the average the most among the measured regions inaccordance with FIG. 3. In the example 8, the region where the Niconcentration was uniform is presented. The column of “percentage ofdeviation from average” presents the percentage of the deviation whenthe Ni concentration deviated from the average the most in the measuredNi concentrations. In the examples 1 to 12, presented is the percentageof the deviation when the Ni concentration deviated from the average themost among the dielectric layers of which the Ni concentrations wereuniform.

The variability in capacitance were examined. Capacitances of 10000samples were measured for each of the examples 1 to 12 and thecomparative examples 1 and 2, and the number of samples of which thecapacitance differs from the average by ±20% or more was examined. Theresult is presented in FIG. 6. The number of capacitance anomaliespresented in FIG. 6 is the number of samples of which the capacitancediffered from the average by ±20% or more in 10000 samples. The doublecircle represents that the number of capacitance anomalies is zero, thecircle represents that the number of capacitance anomalies is one, andthe cross mark represents that the number of capacitance anomalies istwo or greater. In any of the examples 1 to 12, the number ofcapacitance anomalies is small. This is considered because the Niconcentrations in the stacking direction of the five measurement regionsof the dielectric layer 11 became uniform by making the Mg concentrationof the dielectric layer 11 to be equal to or greater than 0 and lessthan 0.002, inhibiting the decrease in permittivity, and thereby thecapacitance of the multilayer ceramic capacitor 100 stabilized. Incontrast, in the comparative examples 1 and 2, the number of capacitanceanomalies increased. This is considered because since the Mgconcentration of the dielectric layer 11 became 0.002 or greater, andthe Ni concentration of the dielectric layer 11 in the stackingdirection did not become uniform, the decrease in permittivity could notbe inhibited and the capacitance of the multilayer ceramic capacitor didnot stabilize.

Moreover, in the examples 1 to 3, 5 to 7, and 9 to 11, the number ofcapacitance anomalies further decreases compared to the examples 4 and8. This is considered because Ni was sufficiently diffused in thedielectric layer 11 by making the thickness of the dielectric layer 11equal to or greater than 0.4 μm and equal to or less than 1.0 the Niconcentration in the dielectric layer 11 was made to be more uniform,and the capacitance of the multilayer ceramic capacitor 100 furtherstabilized.

In the examples 1 to 12, the Ni concentration in a crystal grain and theNi concentration of the crystal grain boundary adjacent to the crystalgrain were measured with the previously described method. The Niconcentration in a crystal grain was within ±20% of the Ni concentrationof the crystal grain boundary adjacent to the crystal grain andtherefore, equal to the Ni concentration of the crystal grain boundaryin all the examples. As described above, in the examples 1 to 12, Nidoes not disproportionately exist in the crystal grain boundary, andtherefore, it can be said that the capacitance stabilizes.

Although the embodiments of the present invention have been described indetail, it is to be understood that the various change, substitutions,and alterations could be made hereto without departing from the spiritand scope of the invention.

What is claimed is:
 1. A multilayer ceramic capacitor comprising: a pairof external electrodes; a first internal electrode that contains a basemetal and is coupled to one of the pair of external electrodes; adielectric layer that is stacked on the first internal electrode andcontains the base metal and a ceramic material mainly composed of bariumtitanate, wherein a main component of the dielectric layer is theceramic material; and a second internal electrode that is stacked on thedielectric layer, contains the base metal, and is coupled to another oneof the pair of external electrodes, wherein a concentration of the basemetal in each of five regions is within ±20% of an average of theconcentrations of the base metal in the five regions, each of the fiveregions including the base metal, the five regions being obtained bydividing a region from a location 50 nm away from the first internalelectrode of the dielectric layer to a location 50 nm away from thesecond internal electrode of the dielectric layer in a stackingdirection between the first internal electrode and the second internalelectrode equally into five, wherein abundance of Ba and Ti in each ofthe five regions is more than 90% as measured by measuring abundance ofBa atoms and Ti atoms by a transmission electron microscope, an atomicconcentration ratio of Mg to Ti is equal to or greater than 0 and lessthan 0.002 in the dielectric layer, and the region located from thelocation 50 nm away from the first internal electrode to the location 50nm away from the second internal electrode includes both a crystal grainof the ceramic material and a crystal grain boundary of the crystalgrain.
 2. The multilayer ceramic capacitor according to claim 1, whereinthe concentration of the base metal in each of the five regions iswithin ±10% of the average of the concentrations of the base metal inthe five regions.
 3. The multilayer ceramic capacitor according to claim1, wherein the concentration of the base metal in each of the fiveregions is within ±5% of the average of the concentrations of the basemetal in the five regions.
 4. The multilayer ceramic capacitor accordingto claim 1, wherein the dielectric layer has a thickness of 0.4 μm orgreater and 1.0 μm or less.
 5. The multilayer ceramic capacitoraccording to claim 1, wherein the ceramic material is BaTiO₃, and thebase metal is Ni.
 6. The multilayer ceramic capacitor according to claim1, wherein a plurality of dielectric layers are stacked across aninternal electrode, and 80% or more of the plurality of dielectriclayers are the dielectric layer.
 7. The multilayer ceramic capacitoraccording to claim 1, wherein the concentration of the base metal ismeasured by TEM (Transmission Electron Microscope).
 8. The multilayerceramic capacitor according to claim 1, wherein the concentration of thebase metal in the crystal grain is within ±20% of the concentration ofthe base metal in the crystal grain boundary.